To avoid risk of adverse effect on an exhaust system including a reducing agent adding system through solidification and accumulation of a reducing agent added to exhaust gas, while realizing a simple and inexpensive constitution.

A control device of an internal combustion engine equipped with an exhaust treatment device for selectively reducing a specific constituent (for instance, NOx) in exhaust by selective reduction catalyst 5 by adding a reducing agent (for instance, urea water) through the medium of a reducing agent adding means (4, 4A) with respect to exhaust discharged from an internal combustion engine (1), includes a heating means (10) on exhaust upstream side of the reducing agent adding means (4, 4A). The reducing agent adding means (4, 4A) or the vicinity thereof is heated to 360°C or higher in a prescribed cycle at least shorter than a regeneration cycle of a diesel particulate filter (3) by the heating means (10), thereby removing the deposite due to the reducing agent.